// 2025/3/26
// 跳台阶

#include <iostream>
using namespace std;

int main() {
    int n; cin >> n;
    int pprev = 0, prev = 0, cur = 1;
    while(n--)
    {
        pprev = prev;
        prev = cur;
        cur = pprev + prev;
    }
    cout << cur << endl;
}
// 64 位输出请用 printf("%lld")